The present invention relates to remote convenience systems, and is particularly directed to systems that have an ability to determine signal strength.
Remote convenience systems are known in the art. Such remote convenience systems permit remote control of certain functions. One example type of a remote convenience system is for remotely controlling vehicle functions. Other example types of remote convenience systems include garage door opener systems and entry light activation systems. Focusing on the remote convenience vehicle systems, remotely controlled vehicle functions include locking and unlocking functions of one or more vehicle doors. A remote convenience system that permits remote locking and unlocking is commonly referred to as a remote keyless entry system. Such remote convenience vehicle systems may provide for control of other vehicle functions. For example, a remote vehicle locator function may be provided. The vehicle locator function causes a horn to emit a horn chirp and/or the headlights of the vehicle to flash xe2x80x9cONxe2x80x9d. This allows a person to quickly locate their car within a crowded parking lot.
Known remote convenience vehicle systems include a receiver/controller unit mounted in an associated vehicle and at least one portable hand-held transmitter unit located remote from the receiver/controller unit. Each transmitter unit is provided with one or more manually actuatable switches. Each switch is associated with a vehicle control function to be performed. The transmitter unit includes circuitry that responds to the actuation of one of the switches to transmit a function request message, along with a security code, in the form of a digital signal. A signal that is received by the receiver/controller unit is processed such that the vehicle performs the requested function.
The remote convenience systems operate in the ultrahigh frequency (UHF) portion of the radio frequency (RF) spectrum. Specifically, the signals from the transmitter units are in the UHF portion of the spectrum that is allocated by the United States Federal Communications Commission (FCC) for unlicensed transmission devices. FCC regulations stipulate that such unlicensed devices cannot have a transmitted signal strength that exceeds a preset maximum. Some countries other than the United States only permit very low levels of transmitted power. The transmitted power level in these countries is lower than the permitted level in the United States. For example, in Japan, remote convenience transmitter units have typical transmission power levels 30 dB below that of a typical United States remote convenience transmitter unit. In addition, within the United States, FCC regulations stipulate that the unlicensed devices must not cause undo radio interference and must operate despite the presence of any radio interference.
Often, it is desirable to accomplish remote control performance of certain functions at a longest possible distance. One example of such a function that is to be performed at the longest possible distance is the remote vehicle locator function. To illustrate such a scenario, consider a shopping mall patron exiting a shopping mall building and being faced with the task of visually locating their car within a vast shopping mall parking lot. It is beneficial to be able to actuate the remote vehicle locator function from a location near the exit door of the shopping mall, before proceeding into the parking lot.
Another example of a remote function that is to be performed at a longest possible distance is the door lock function. Thus, if an operator has forgotten to lock the vehicle doors and has proceeded away from the vehicle, the doors can be locked without returning to the vehicle.
For some remote control functions, it is desirable to permit performance only when the operator is relatively near the vehicle. One example of a remote function that is to be performed only when the operator is near to the vehicle is the door unlock function. Thus, the vehicle is unlocked only when the operator is near enough to see activity that occurs at the vehicle.
Distance is related to received signal strength. Thus, by determining signal strength, appropriate control can be accomplished.
In accordance with one aspect, the present invention provides an apparatus for determining signal strength of a received electromagnetic signal comprised of a plurality of pulses that convey a remote convenience function request, and for causing performance of the requested function. A comparator has a first input for receiving an electrical signal with a voltage that varies to convey the remote convenience function request. A second input of the comparator receives a threshold voltage value. An output of the comparator provides an output signal indicative of the occurrence of the voltage of the electrical signal exceeding the threshold value. Means adjusts the threshold voltage value. Means monitors the output signal of the comparator during adjustment of the threshold voltage value to determine strength of the electromagnetic signal.
In accordance with another aspect, the present invention provides a method of determining signal strength of an electromagnetic signal, that is comprised of a plurality of pulses that convey a remote convenience function request and that is intended for causing performance of the requested function. An electrical signal, which has a voltage that varies to convey the remote convenience function request, is compared with a threshold voltage value. An output signal that is indicative of the occurrence of the voltage of the electrical signal exceeding the threshold value is output. The threshold voltage value is adjusted. The output signal is monitored during adjustment of the threshold voltage value to determine strength of the electromagnetic signal.